How Long Does Metronidazole Stay In The Body?

In our latest question and answer, the pharmacist discusses how long Flagyl (metronidazole) lasts in the body.

Question

How long does it take for the total removal of metronidazole and its metabolites from the body? I have taken metronidazole for 7 days for Trichomonas intestinalis. This is the second day after ending the full dose I have been administered. But until now, I have had side effects, like nausea, vomiting, headache, and decreased libido... I'm wondering when its' effects will stop.

Asked by Valesibo On Sep 22, 2022

Answered by
Medical Content Reviewed By HelloPharmacist Staff

Published Sep 22, 2022
Last updated Sep 22, 2022

Key points

  • Metronidazole takes around 2 to 3 days after your last dose to be completely metabolized and eliminated from your system.

Answer

Thanks for your question!

Metronidazole is metabolized and eliminated from the body completely around 2 to 3 days after your last dose. I describe this in more detail in the sections below.

What Is Metronidazole?

Metronidazole (brand name Flagyl) is an antibiotic and antiprotozoal agent that is used for a variety of indications including pneumonia, respiratory infections, intra-abdominal infections, and bacterial vaginosis. 

Once taken by mouth, metronidazole is quickly absorbed and reaches peak concentration in the blood after one to three hours. When taken with food, the rate of absorption decreases but not the overall extent of absorption. The overall effect of metronidazole when taken with food, however, is unchanged.

Metronidazole Metabolism

Metronidazole is mostly metabolized in the liver and is excreted via the urine and feces.

Per the prescribing information, the half-life (time for 50% of the drug to be metabolized) is about 8 hours. A general rule of thumb is that it takes about 5 half-lives for a drug to be considered completely metabolized. Therefore, it should take about 2 to 3 days for metronidazole to be completely eliminated from the body.

If metronidazole is causing side effects, such as nausea, diarrhea, or vomiting, you can expect them to resolve a few hours after dosing, or at the very latest, within a few days after the last dose was taken. 

Avoid Alcohol With Metronidazole

One of the major precautions with metronidazole is the need to avoid alcohol consumption while taking the drug. Metronidazole can alter the metabolism of alcohol and increase the amount of a toxic metabolite, acetaldehyde. The use of alcohol and metronidazole together can cause a "Disulfiram-like" reaction. Potential side effects include:

  • Nausea
  • Vomiting
  • Increased heart rate
  • Headache
  • Flushing
  • Abdominal cramps

Generally, it is recommended to avoid alcohol and alcohol-containing products (e.g cough medications with alcohol) during and for up to 3 days after the last dose of metronidazole.

Final Words

Thanks again for your question and reach back out anytime!

References

  • Metronidazole Prescribing Information, AccessFDA
  • Overview of pharmacokinetics, PubMed

About the Pharmacist

Dr. Brian Staiger, PharmD

Dr. Brian has been practicing pharmacy for over 11 years and has wide-ranging experiences in many different areas of the profession. From retail, clinical and administrative responsibilities, he's your knowledgeable and go-to source for all your pharmacy and medication-related questions! Feel free to send him an email at Hello@HelloPharmacist.com! You can also connect with Dr. Brian Staiger on LinkedIn.

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